5cddc1460e
Config provides a way to concurrently access Width and Height. Register provides a way for packages to run code on app state change without plumbing changes all the way to the process main function. This is motivated by gl/glutil.Image which needs to rebuild its textures on start/stop and can be deeply nested. (See golang.org/cl/9707 for the followup.) Tested manually on android and darwin/amd64. Doing this kind makes it clear any CL modifying this code needs a lot of manual testing right now, so some kind of trybot support is something I'm going to prioritise. Fixes golang/go#10686 Fixes golang/go#10461 Fixes golang/go#10442 Fixes golang/go#10226 Updates golang/go#10327 Change-Id: I2882ebf3995b6ed857cda823e94fbb17c54b43a8 Reviewed-on: https://go-review.googlesource.com/9708 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
118 lines
4.2 KiB
Go
118 lines
4.2 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/*
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Package geom defines a two-dimensional coordinate system.
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The coordinate system is based on an left-handed Cartesian plane.
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That is, X increases to the right and Y increases down. For (x,y),
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(0,0) → (1,0)
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↓ ↘
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(0,1) (1,1)
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The display window places the origin (0, 0) in the upper-left corner of
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the screen. Positions on the plane are measured in typographic points,
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1/72 of an inch, which is represented by the Pt type.
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Any interface that draws to the screen using types from the geom package
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scales the number of pixels to maintain a Pt as 1/72 of an inch.
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*/
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package geom // import "golang.org/x/mobile/geom"
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/*
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Notes on the various underlying coordinate systems.
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Both Android and iOS (UIKit) use upper-left-origin coordinate systems
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with for events, however they have different units.
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UIKit measures distance in points. A point is a single-pixel on a
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pre-Retina display. UIKit maintains a scale factor that to turn points
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into pixels. On current retina devices, the scale factor is 2.0.
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A UIKit point does not correspond to a fixed physical distance, as the
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iPhone has a 163 DPI/PPI (326 PPI retina) display, and the iPad has a
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132 PPI (264 retina) display. Points are 32-bit floats.
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Even though point is the official UIKit term, they are commonly called
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pixels. Indeed, the units were equivalent until the retina display was
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introduced.
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N.b. as a UIKit point is unrelated to a typographic point, it is not
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related to this packages's Pt and Point types.
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More details about iOS drawing:
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https://developer.apple.com/library/ios/documentation/2ddrawing/conceptual/drawingprintingios/GraphicsDrawingOverview/GraphicsDrawingOverview.html
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Android uses pixels. Sub-pixel precision is possible, so pixels are
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represented as 32-bit floats. The ACONFIGURATION_DENSITY enum provides
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the screen DPI/PPI, which varies frequently between devices.
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It would be tempting to adopt the pixel, given the clear pixel/DPI split
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in the core android events API. However, the plot thickens:
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http://developer.android.com/training/multiscreen/screendensities.html
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Android promotes the notion of a density-independent pixel in many of
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their interfaces, often prefixed by "dp". 1dp is a real physical length,
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as "independent" means it is assumed to be 1/160th of an inch and is
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adjusted for the current screen.
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In addition, android has a scale-indepdendent pixel used for expressing
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a user's preferred text size. The user text size preference is a useful
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notion not yet expressed in the geom package.
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For the sake of clarity when working across platforms, the geom package
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tries to put distance between it and the word pixel.
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*/
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import "fmt"
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// Pt is a length.
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//
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// The unit Pt is a typographical point, 1/72 of an inch (0.3527 mm).
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//
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// It can be be converted to a length in current device pixels by
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// multiplying with PixelsPerPt after app initialization is complete.
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type Pt float32
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// Px converts the length to current device pixels.
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func (p Pt) Px() float32 { return float32(p) * PixelsPerPt }
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// String returns a string representation of p like "3.2pt".
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func (p Pt) String() string { return fmt.Sprintf("%.2fpt", p) }
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// Point is a point in a two-dimensional plane.
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type Point struct {
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X, Y Pt
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}
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// String returns a string representation of p like "(1.2,3.4)".
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func (p Point) String() string { return fmt.Sprintf("(%.2f,%.2f)", p.X, p.Y) }
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// A Rectangle is region of points.
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// The top-left point is Min, and the bottom-right point is Max.
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type Rectangle struct {
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Min, Max Point
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}
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// String returns a string representation of r like "(3,4)-(6,5)".
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func (r Rectangle) String() string { return r.Min.String() + "-" + r.Max.String() }
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// PixelsPerPt is the number of pixels in a single Pt on the current device.
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//
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// There are a wide variety of pixel densities in existing phones and
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// tablets, so apps should be written to expect various non-integer
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// PixelsPerPt values. In general, work in Pt.
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//
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// Not valid until app initialization has completed.
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var PixelsPerPt float32
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// Width is deprecated. Use app.GetConfig().Width.
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var Width Pt
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// Height is deprecated. Use app.GetConfig().Height.
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var Height Pt
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